Wow, if ever there was a subject for my wife on flyertalk, this would be it! Unfortunately she is out of town for a couple of weeks, but I'm pretty sure I know what she puts in her yogurt marinade, She uses plain yogurt, a paste she makes of fresh coriander and serrano peppers ground together (with the seeds taken out), fresh mint, ginger (not 100% sure on this), salt, ground cumin and turmeric.
She usually marinades the chicken overnight and serves it with homemade naan, mint sauce and a tomato and onion salad and my "grilling out beer" (Blatz).
We also try marinading the chicken in yogurt and Nando's peri-peri sauce when we get a Nando's craving and know it will be a couple of months till we can visit one!